Added value for the environment: monitoring production, reducing rejects

Plastics and their diversity can exert a certain fascination. This was also the case for Nele Zerhusen: she was already captivated by this topic during her school days. A few years later, in her Bachelor's thesis, she researched how plastics can be further developed for the benefit of the environment. Her outstanding work was eventually honoured with the award of the Deutsche Kautschuk Gesellschaft (German Rubber Society).

In an interview with K-MAG Nele Zerhusen talks about what fascinates her about research on plastics, what the results of her research mean for industry and how she sees plastics research developing further.

Why did you decide to study materials science?

Nele Zerhusen: Even in my school days, I was particularly interested in chemistry and physics, so I did my school internship at a plastics processing company in the laboratory. It soon became clear that I wanted to study natural sciences or engineering. A friend introduced me to the dual study programme at Pöppelmann. What I particularly liked about the course was that the content included both chemical and physical modules that were directly related to practice. What fascinates me most about plastics is the diversity and the possible applications.

What was your thesis about and what was the result?

Zerhusen: In the last two decades, the technology for the generation and detection of terahertz radiation has been developed considerably, so that the special properties of the radiation could be utilised. Only a few years ago, TeraTonics introduced the STRIPP sensor for inline control using terahertz radiation. In my bachelor thesis I compared this new and fast approach of terahertz time domain spectroscopy with X-ray computed tomography (CT).

The methods were compared on the basis of images of a component from thermoplastic foam injection moulding (TSG) processing. The evaluation criteria were density distribution, cell structure, size and distribution, over the entire component as well as individual component dimensions. The result is that the measurement method must be selected according to the application and the problem.

The single shot terahertz time domain spectroscopy with the STRIPP sensor from TeraTonics S.A.S. works with a measuring speed of 500 cm2/30s and can be used directly at the injection moulding machine. The terahertz radiation is not ionising, so that safety precautions with regard to the Radiation Protection Ordinance can be dispensed with. These factors and the small size of the sensor itself allow 100-percent-monitoring of the series. Another argument in favour of the STRIPP sensor is its comparatively low cost.

The images of the sensor have a good spatial resolution, making it possible to map the density distribution or detect potential defects. The resolution of the sensor is limited by the wavelength of the terahertz radiation, so that CT must be used for measurements of higher resolutions. CT, in turn, is quite expensive to purchase and maintain, especially for industrial components that often require a large sample volume.

What do the results of your research mean for the Pöppelmann company?

Zerhusen: Through this project, I had the opportunity to better understand the technology in depth, to test the possible applications and to gain initial experience with the sensor at TeraTonics. In this way, I was able to gain a lot of information about the technology for the company, so that the possible applications for various projects can be assessed.

What makes the measuring technology using STRIPP sensors innovative and what added value does it offer plastics processors?

Zerhusen: This sensor opens up the possibility of 100-percent-monitoring of various components in series production. As the measuring device is non-ionising and harmless to health, no corresponding safety precautions need to be taken.

To what extent does measurement technology help to better use or develop plastics in terms of a circular economy?

Zerhusen: The STRIPP sensor is intended as an inline control of plastic components and is not part of the circular economy. However, the technology enables 100-percent-monitoring in series production. Errors in the process, for example deviations in the cell distribution in the TSG, can be detected at an early stage. In connection with Industry 4.0, the STRIPP sensor will provide real time feedback to the production systems in the future. This will result in a reduction in rejects.

How do you think research around plastics and circular economies will continue to develop?

Zerhusen: Society's awareness of the environment has changed a lot in recent years. The plastic waste in the oceans and on the land results in a negative image of plastics. To reduce more plastics in the environment, plastic waste should be reduced or reused. To reduce plastic waste, processes should be designed with minimal waste. This includes the optimisation of equipment, for example through the STRIPP sensor, and the reuse of in-process waste, such as sprues.

In my opinion, the possibilities of recycled material have not been fully exhausted. To increase this use, we need to make more plastic articles recyclable and increase customer confidence in post consumer materials (PCR).

In order for plastic articles to be recyclable, it is necessary to exert influence already in the development process. One example is the trend to design yoghurt cups made of polypropylene (PP) with a cardboard label. The PP cup can be recycled without any problems. However, the cardboard label must be removed before disposal. If this is not done, the recycling of the cup is more difficult. These obstacles to recycling should be avoided in the development of the packaging.

Especially in the pharmaceutical and medical sector, the use of PCR is not possible due to various standards and regulations. In order to increase customer confidence in the material, various tests are necessary. These include analyses of the structure and composition, the determination of various characteristic values and the establishment of incoming goods controls. I think that the interest in PCR material will continue to grow in the future. This is an important step towards reducing the carbon footprint.